1. Field of the Invention
This invention concerns a variable-capacity turbocharger which can control an amount of exhaust gas provided into a turbine compartment by operating nozzle vanes. More specifically, the invention concerns an improvement of a nozzle drive mechanism to transmit to the nozzle vanes a displacement of an actuator which operates the nozzle vanes.
2. Description of the Related Art
A turbocharger is an effective means to increase the output of an internal combustion engine. A turbine is rotated by exhaust gas from the engine, and a compressor mounted on a same shaft as turbine pressurizes the air supplied to the engine. Turbochargers are currently installed in a variety of engines. However, the flow rate of the exhaust gas varies with the speed of the engine revolution. The flow rate of the exhaust gas, which is actually supplied from the engine, will not always be in the amount that needed to produce the ideal operating conditions for the supercharger. To rectify this situation and allow the turbocharger capacity to be used to its best advantage, the variable-capacity turbocharger has been developed. In a variable-capacity turbocharger, the flow of the exhaust gas in the turbine compartment is regulated according to the operating state of the internal combustion engine.
This sort of variable turbocharger has a number of nozzle vanes in a nozzle unit of the turbine, which is inside a housing. The nozzle vanes provided on a nozzle shaft are supported in such a way that they can rotate between open and closed positions. The nozzle shaft is connected through a lever to a link plate which has a doughnut shape. The link plate rotates freely on the rotary axis of the turbine. An actuator on the outside of the housing causes the link plate to rotate by means of a transmission mechanism. When the link plate rotates, the nozzle vanes operate synchronously, continuously moving between the open and closed positions to adjust the degree of opening of the nozzle vanes.
In the nozzle drive mechanism to drive the nozzle vanes according to the prior art, the rotary action of the link plate is not transmitted smoothly into the rotary action of the nozzle vanes. To achieve the desired action of the link plate, the actuator on the outside of the housing of the variable turbocharger had to be large enough to produce an appropriate force.
The technical problem which this invention addressed is to solve the above-mentioned shortcoming in the prior art. The object of this invention is to provide a nozzle drive mechanism for the link plate, which can operate all the nozzle vanes smoothly and synchronously.
The variable-capacity turbocharger which controls the opening degree of the nozzle vanes according to this invention has a turbine provided in a housing, which is free to rotate on a turbine shaft, a plurality of nozzle vanes arranged in nozzle units around the turbine in the housing, a link plate which rotates freely around the turbine provided in the housing, and which is connected to the nozzle vanes by levers and continuously moves the nozzle vanes synchronously between the open and closed positions and an actuator outside the housing, which is connected to the link plate through a transmission mechanism.
The invention disclosed in the first preferred embodiment is a variable turbocharger which is distinguished by the following.
The nozzle vanes are supported in such a way that the nozzle vanes are free to rotate between the open and closed positions on nozzle shafts. The nozzle vanes are connected to levers which correspond to the nozzle shafts so as to rotate along with the levers, and each boss at the end of each lever is provided with a shaft which is parallel to the nozzle shaft. The shafts in the nozzle vanes engage in oblong holes in the link plate in such a way that they are free to swing, and are thereby connected to the link plate. A declined straight or curved centerline which runs through oblong hole to the oblong direction, extends at a given angle with respect to the radius of the link plate.
With the invention disclosed above, the oblong holes in the link plate which receive the shafts of the levers extend in the axial direction at a given angle with respect to the radius of the link plate as defined by its rotational center. Thus, when the link plate rotates, there is a component in the generated force which acts on the link plate at the point of contact of the shaft with the hole which pushes the shaft in the radial direction. The shafts of the levers can move smoothly in the radial direction within the holes in the link plate, and the link plate can operate easily.
The invention disclosed in a second preferred embodiment has curved oblong hole. The curved centerline which runs the oblong hole to the oblong direction, is curved along an arc tangent to the declined straight line extending at a given angle with respect to the radius of the link plate.
With the invention disclosed above, each of the oblong holes in the link plate which receive the shafts of the levers is curved along an arc tangent to a line extending at a given angle with respect to one of the radii from the rotational center of the link plate. When the link plate rotates, the component of the pushing force on the shaft which acts in the radial direction is greater than that of the invention disclosed in the first preferred embodiment of this application. This allows the shafts of the levers to move more smoothly in the radial direction within the holes in the link plate.